1. Field of the Invention
The present invention relates to low dielectric constant materials such as insulating films (dielectrics) used between LSI element layers, etc., and to their production and use.
2. Description of the Related Art
With higher speeds and higher integration of LSI elements, signal delays are becoming an ever more serious problem. Signal delays are related to the product of the wiring resistance R and the capacity C between the wirings and between layers, and an effective means of minimizing delays involves lowering the wiring resistance while also reducing the relative dielectric constant of the interlayer dielectrics. By the year 2001, it is said that higher integration will result in wiring spacings of about 0.18 xcexcm, thus requiring materials with a relative dielectric constant of less than 2.5.
Previously known methods form films as interlayer dielectrics by a spin-on-glass (SOG) process using sols prepared by hydrolyzing tetraalkoxysilanes. However, the molecular structures of materials fabricated in this fashion have absolutely no voids in their three-dimensional network structures of xe2x89xa1Sixe2x80x94Oxe2x80x94Sixe2x89xa1, and their relative dielectric constants have been as high as 4.0. Some methods proposed for lowering the relative dielectric constant involve CVD for formation of SiOF films, formation of organic material films, and porous film formation. The relative dielectric constant of SiOF reduces to about 3.3 as the F content increases, but higher moisture absorption with greater F content has been a problem. Organic materials are low dielectric constant materials with relative dielectric constants of down to about 2.2, but their problems include poor heat resistance and low adhesion to substrates. In organic SOG systems, introduction of organic groups into SiO2 has been investigated to achieve lower density and lower the relative dielectric constant, but the limit is said to be about 2.7. On the other hand, porous materials have variable relative dielectric constants depending on the amount of pores, and they are therefore promising as materials offering relative dielectric constants lower than 2.5.
One example of a porous material has been reported where inorganic SOG is reacted with a silylating agent to form a film and then the silylating agent is heat treated to decomposition to introduce approximately 80-nm pores, by which the relative dielectric constant has been lowered to 2.3 [N. Aoi, Jpn. J. Appl. Phys. 36(1997) 1355]. This film, however, has an increase of about 13% in the dielectric constant due to moisture absorption in air, while the introduced pores are also large so that only an average of 2 pores are present in a gap of 0.18 xcexcm between wiring, and thus film strength is therefore a problem.
Another example of a porous film is a fine porous xerogel film obtained by forming a film of a solution made from tetraethoxysilane as the starting material, aging it under a controlled atmosphere, performing solvent substitution with a low surface tension solvent, drying it in such a manner that the film does not contract upon evaporation of the solvent, and treating the surface with a silylating agent [Mat. Res. Soc. Symp. Proc. 443, 99(1997)]. However, the xerogel not only has a complicated fabrication process but strict control is necessary for each step in the process, and therefore lack of reproducibility for actual device fabrication is thought to be one of its drawbacks. The basic backbone of the film is composed of a SiO4 tetrahedron. The backbone interior is composed of only the SiO4 tetrahedron, but because of the organic groups introduced by the silylating agent, organic groups substitute for some of the oxygens of the SiO4 tetrahedrons only around the pores and on the surface.
Films formed from hydrogenated silica fine particles with surface Sixe2x80x94H bonds and modified with hydrogen silsesquioxane (HSQ) have been reported as materials with relative dielectric constants of less than 2.5 [Muraguchi et al., 58th Symposium of the Association of Applied Physics, Lecture Summary No.2, 4p-K-7]. However, the heat resistance of Sixe2x80x94H is not very high, as escape of hydrogen begins from 400xc2x0 C. and is marked at 450xc2x0 C. and above. Once hydrogen is released, the moisture absorption of the film begins to increase. Since the annealing temperature for metal wiring in LSI processes is said to be 450xc2x0 C., this film would be expected to pose a problem when applied to such processes.
It is an object of the present invention to provide silica-based materials with low moisture absorption and a low dielectric constant, which can be applied for semiconductor elements and electrical circuit parts.
This object is achieved by the invention as described below.
1. A silica-based porous film having a three-dimensional network structure containing a siloxane skeleton comprising a SiO4 tetrahedron structural unit, the silica-based porous film including on the surface and in the interior a backbone wherein at least one of the crosslinked oxygens of some or all of the SiO4 tetrahedron structural units are replaced with organic groups, and having fine voids with an average size of no greater than 10 nm, preferably no greater than 5 nm, more preferably no greater than 2 nm, especially no greater than 1 nm the direct perimeters of which are surrounded with the backbone containing organic group-substituted tetrahedron structural units.
2. A silica-based porous film according to 1. above which includes in the three-dimensional network structure at least one element selected from the group consisting of B, Al, Ge, Ti, Y, Zr, Nb and Ta as an inorganic component in addition to Si and O.
3. A silica-based porous film according to 1. or 2. above, which contains at least a methyl group and/or phenyl group as the organic group.
4. A silica-based porous film according to any one of 1. to 3. above, which includes in the three-dimensional network structure at least one element selected from the group consisting of B, Al, Ge, Ti, Y, Zr, Nb and Ta as an inorganic component in addition to Si and O and which contains at least a methyl group and/or phenyl group as the organic group, wherein the molar ratio of the inorganic component element other than Si and O with respect to Si is from 0.005 to 0.15, and the molar ratio of the methyl group and/or phenyl group with respect to Si is from 0.6 to 1.5.
5. A silica-based porous film according to any one of 1. to 4. above, wherein the specific surface area according to BET is at least 100 m2/g and the contact angle of water is at least 90xc2x0.
6. A silica-based porous film according to 2. above, wherein the molecular structure of the main chain in the three-dimensional network structure includes at least one selected from among molecular structure (1): a ring structure, molecular structure (2): a structure wherein ring structure units including ladder-like structures and polyhedral structures are linked in two or three dimensions, and molecular structure (3): a linked chain structure which is crosslinked with at least two of the aforementioned structures and has no uncrosslinked ends.
7. A silica-based porous film according to 2. above, wherein the chemical structure of the terminal portion of the main chain in the three-dimensional network structure is xe2x80x94Oxe2x80x94Mxe2x80x2Rxe2x80x21Rxe2x80x22 . . . Rxe2x80x2nxe2x88x921 (where Rxe2x80x21, Rxe2x80x22 . . . Rxe2x80x2nxe2x88x921 are terminal groups and n is the valency of element Mxe2x80x2), and the difference in electronegativity for all the bonded atom pairs of the Mxe2x80x2Rxe2x80x21 . . . Rxe2x80x2nxe2x88x921 portion is no greater than 0.7.
8. A semiconductor device including a silica-based porous film according to any one of 1. to 7. above as an interlayer dielectric.
9. A process for production of a silica-based porous film, which comprises heat treating a silica-based film with at least two different organic groups bonded to Si having at least two different pyrolytic temperatures (T1, T2: T1 greater than T2) and with SiO2 as the main inorganic component, in an inert gas atmosphere at a temperature intermediate between T1 and T2, and decomposing the organic groups that have pyrolytic temperature T2 without decomposing the organic groups that have pyrolytic temperature T1, to form voids with an average size of no greater than 10 nm in a three-dimensional network structure including a siloxane backbone.
10. A process for production of a silica-based porous film according to 9. above, wherein the organic groups that thermally decompose to form voids are alkyl groups of 2 or more carbon atoms or fluoro-substituted forms thereof, and the organic groups that remain in the film without being thermally decomposed are methyl groups or phenyl groups.
11. A silica-based porous film-forming coating solution which includes a solution obtained by dissolving (A1) a compound represented by the general formula R1Si(OR)3 or R1SiX3 (where R1 is a methyl group or phenyl group, R is an alkyl group of 1-4 carbon atoms or a phenyl group, and X is a halogen element other than F) and (B1) a compound represented by the general formula R2R3Si(OR)2 or R2R3SiX2 (where R2 and R3 each is an alkyl group of 2 or more carbon atoms or a fluoro-substituted form thereof, or a methyl group or phenyl group, provided that at least one of R2 and R3 is an alkyl group of 2 or more carbon atoms or a fluoro-substituted form thereof, R is an alkyl group of 1-4 carbon atoms or a phenyl group, and X is a halogen element other than F) in an organic solvent followed by hydrolysis.
12. A silica-based porous film-forming coating solution which includes a solution obtained by dissolving (A2) a compound represented by the general formula R4Si(OR)3 or R4SiX3 (where R4 is an alkyl group of 2 or more carbon atoms or a fluoro-substituted form thereof, R is an alkyl group of 1-4 carbon atoms or a phenyl group, and X is a halogen element other than F) and (B2) a compound represented by the general formula R5R6Si(OR)2 or R5R6SiX2 (where R5 and R6 are methyl and/or phenyl groups, R is an alkyl group of 1-4 carbon atoms or a phenyl group, and X is a halogen element other than F) in an organic solvent followed by hydrolysis.
13. A silica-based porous film-forming coating solution which includes a solution obtained by dissolving (A1) a compound represented by the general formula R1Si(OR)3 or R1SiX3 (where R1 is a methyl group or phenyl group, R is an alkyl group of 1-4 carbon atoms or a phenyl group, and X is a halogen element other than F) and (A2) a compound represented by the general formula R4Si(OR)3 or R4SiX3 (where R4 is an alkyl group of 2 or more carbon atoms or a fluoro-substituted form thereof, R is an alkyl group of 1-4 carbon atoms or a phenyl group, and X is a halogen element other than F) in an organic solvent followed by hydrolysis.
14. A silica-based porous film-forming coating solution according to any one of 11. to 13. above, wherein the coating solution contains a compound represented by the general formula M(OR)n or MXn (where M is at least one metal element selected from the group consisting of B, Al, Ge, Ti, Y, Zr, Nb, Ta and Si, n is the number of equivalences of the metal element, R is an alkyl group of 1-4 carbon atoms or a phenyl group, and X is a halogen element other than F), the molar ratio of M to Si is from 0.005 to 0.15, and the molar ratio of alkyl groups and/or phenyl groups to Si is from 0.6 to 1.5.
15. A silica-based porous film-forming coating solution according to 11. to 14. above, wherein the solute in the coating solution has a weight average molecular weight of less than 5,000, preferably less than 3,000, more preferably less than 1,000, especially less than 500.
16. A process for production of a silica-based porous film which comprises coating a solution according to any one of 11. to 15. above and then drying it at a temperature of from 70xc2x0 C. to 300xc2x0 C., heat treating it at a temperature of from 350xc2x0 C. to 650xc2x0 C. in an inert gas atmosphere and thermally decomposing the alkyl groups of 2 or more carbon atoms or their fluoro-substituted forms.
17. A low dielectric constant material comprising a compound with units represented by M(xe2x80x94Oxe2x80x94)n, R1Si(xe2x80x94Oxe2x80x94)3 and R2R3 Si(xe2x80x94Oxe2x80x94)2 (where M is at least one metal element selected from among B, Al, Ge, Ti, Y, Zr, Nb, Ta and Si, n is the number of equivalences of the metal M, R1, R2 and R3 each represent an alkyl group, aryl group or aralkyl group, and CF bonds are substituted for some or all of the CH bonds in R1 and/or R2).
18. A low dielectric constant material according to 17. above, wherein some or all of the R2 groups are (CH2)l(CF2)mCF3 (where l and m are integers of from 0 to 10), R1 and R3 are methyl groups, and when R2 groups other than (CH2)l(CF2)mCF3 are present, those R2 groups are methyl groups.
19. A low dielectric constant material according to 17. or 18. above, wherein the molar ratio of the metallic element M of M(xe2x80x94Oxe2x80x94)n with respect to all the metallic elements is from 0.04 to 0.40, the molar ratio of Si directly bonded to alkyl groups, aryl groups or aralkyl groups wherein CF bonds are substituted for some or all of the CH bonds with respect to the total Si is from 0.15 to 0.6, and the molar ratio of alkyl groups, aryl groups or aralkyl groups with respect to the total Si is from 0.5 to 1.7.
20. An insulating film-forming coating solution which includes a solution obtained by dissolving a compound represented by
(A) M(OR4)n,
(B) R1Si(OR5)3 and/or Rxe2x80x31Si(OR7)3, or
(C) R2R3Si(OR6)2 and/or R2Rxe2x80x33Si(OR8)2 
(Where M is at least one metal element selected from among B, Al, Ge, Ti, Y, Zr, Nb, Ta and Si, n is the number of equivalences of the metal M, R1, R2 and R3 are each an alkyl group, aryl group or aralkyl group, R4, R5, R6, R7 and R8 are each an alkyl group or phenyl group, and Rxe2x80x31 and Rxe2x80x33 are each an alkyl group, aryl group or aralkyl group wherein CF bonds are substituted for some or all of the CH bonds), in an organic solvent followed by hydrolysis.
21. A semiconductor device that employs an interlayer dielectric comprising a low dielectric constant material according to any one of 17. to 19. above.
22. A low dielectric constant material comprising a compound having a unit represented by M(xe2x80x94Oxe2x80x94)n (where n is the number of equivalences of the metal M) with at least one metallic element M selected from among B, Al, Ge, Ti, Y, Zr, Nb and Ta and oxygen, and one or more Si units including at least one unit from among R1Si(xe2x80x94Oxe2x80x94)3 and R2R3Si(xe2x80x94Oxe2x80x94)2 of the three different Si units represented by Si(xe2x80x94Oxe2x80x94)4, R1Si(xe2x80x94Oxe2x80x94)3 and R2R3Si(xe2x80x94Oxe2x80x94)2 (where R1, R2 and R3 are alkyl groups, aryl groups or aralkyl groups), such that when only the Si unit R1Si(xe2x80x94Oxe2x80x94)3 is included some of R1 groups are replaced with H, and when only the Si unit R2R3Si(xe2x80x94Oxe2x80x94)2 or both the Si units R1Si(xe2x80x94Oxe2x80x94)3 and R2R3Si(xe2x80x94Oxe2x80x94)2 are included, some or all of the R1 and/or R2 groups are replaced with H.
23. A low dielectric constant material according to 22. above, which includes at least the unit R2R3Si(xe2x80x94Oxe2x80x94)2 of the three different Si units represented by Si(xe2x80x94Oxe2x80x94)4, R1Si(xe2x80x94Oxe2x80x94)3 and R2R3Si(xe2x80x94Oxe2x80x94)2 (where R1, R2 and R3 are alkyl groups, aryl groups or aralkyl groups), wherein some or all of the R2 groups of the units are replaced with H and the R3 groups of the units HR3Si(xe2x80x94Oxe2x80x94)2 in which R2 has been replaced with H are methyl groups.
24. A low dielectric constant material according to 22. or 23. above, wherein the molar ratio of Si with respect to the total metal elements is from 0.57 to 0.95, the molar ratio of Si directly bonded to hydrogen with respect to the total Si is 0.3 or greater, and the molar ratio of alkyl groups, aryl groups or aralkyl groups with respect to the total Si is from 0.5 to 1.7.
25. An interlayer dielectric comprising a low dielectric constant material according to any one of 22. to 24. above.
26. An IC chip comprising a low dielectric constant material according to any one of 22. to 24. above.